fix: adjust file paths of subcontent for /cpp/language/functions

Author: Sudrut

src/content/docs/cpp/language/default_arguments.mdx renamed to src/content/docs/cpp/language/functions/default_arguments.mdx

@@ -1,7 +1,7 @@
 ---
 title: Default arguments
 cppdoc:
-  keys: ["cpp.lang.default_arguments"]
+  keys: ["cpp.lang.functions.default_arguments"]
 ---
 
 import { Decl, DeclDoc } from "@components/decl-doc";

src/content/docs/cpp/language/function.mdx renamed to src/content/docs/cpp/language/functions/function.mdx

@@ -1,7 +1,7 @@
 ---
 title: Function declaration
 cppdoc:
-  keys: ["cpp.lang.function"]
+  keys: ["cpp.lang.functions.function"]
 ---
 
 import { Decl, DeclDoc } from "@components/decl-doc";

src/content/docs/cpp/language/variadic_arguments.mdx renamed to src/content/docs/cpp/language/functions/variadic_arguments.mdx

@@ -1,7 +1,7 @@
 ---
 title: Variadic arguments
 cppdoc:
-  keys: ["cpp.lang.variadic_arguments"]
+  keys: ["cpp.lang.functions.variadic_arguments"]
 ---
 
 import { Decl, DeclDoc } from "@components/decl-doc";